This invention relates to ultrasonic transducers, and more particularly to an ultrasonic probe having a backing member for use in ultrasonic imaging systems.
A conventional ultrasonic probe generally comprises a linear array of piezoelectric transducer elements for transmission of an ultrasonic wave into a body under examination in response to electrical signals from a control circuit and reception of echo waves returning from structural discontinuities within the body. If required, an acoustic lens is provided at the energy entry surface of the transducer. A backing member is secured to the rear of the transducer array to absorb undesired ultrasonic energy emitted backward. It is required that the backing member be composed of a material having a sufficient amount of hardness to give structural integrity to the transducer array and a high degree of precision, consistent physical properties, a large value of acoustic energy absorption coefficient to keep the probe compact and lightweight, and a desired acoustic impedance to ensure against reduction in sensitivity of the ultrasonic transducers.
A known backing member is composed of a mixture of tungsten particles and ferrite rubber or plastic having a Shore-A hardness greater than 85, and an acoustic impedance of greater than 6.times.10.sup.5 g/cm.sup.2. sec. Although satisfactory in mechanical strength, this backing member is not satisfactory in the performance of energy absorption due to the small difference in acoustic impedance between it and the piezoelectric elements.
Another known backing member is composed of a mixture of silicone rubber and alumina oxide having an acoustic impedance greater than 1.5.times.10.sup.5 g/cm.sup.2. sec and ultrasonic absorption coefficient greater than about 1.5 dB/mm at 3MHz. Although satisfactory in absorption performance, this material is not satisfactory in mechanical strength.
Therefore none of the conventional backing members satisfy both the strength and absorption requirements.